Cathodoluminescent light sources are known as shown in United Kingdom patents, GB No. 2,089,516 published 23 June 1982 and GB No. 2,070,849 published 9 Sept. 1981. These light sources employ thermionic cathodes as an electron source which substantially limits the efficiency of the lamp as well as the operating life thereof. Large-scale cathodoluminescent displays, such as cathode ray tubes, also are known which include a cathodoluminescent layer at the face of the screen and an electron beam from a thermionic cathode. Small-scale cathodoluminescent displays also are known as shown in U.S. Pat. No. 3,855,499, Yamada et al., which display includes a plurality of cathodoluminescent phosphor dots at the display face and a plurality of field emission cathodes. For each phosphor dot there is an associated cathode such that electrons from only a single cathode impinge upon a phosphor dot. Groups of cathodes are interconnected to provide for the display of line segments at the face of the display. The number of electrons emitted by a single field emission cathode along a relatively narrow beam is limited thereby greatly limiting the brightness of such a display. Also, displays are not intended for general illumination purposes.
An object of this invention is the provision of a high efficiency cathodoluminescent lamp which avoids many of the shortcomings of prior art cathodoluminescent lamps such as described above.
An object of this invention is the provision of an improved cathodoluminescent lamp in which a very large percentage of the electrical input to the lamp is converted to light energy for high efficiency operation.
An object of this invention is the provision of an improved cathodoluminescent lamp of the above-mentioned type which has a long operating life and is inexpensive to manufacture as well as to operate.
The above and other objects and advantages of this invention are achieved by use of an evacuated envelope at least a portion of which is light-transmitting. A layer of phosphor and an anode electrode comprising a conducting layer in surface engagement with the phosphor layer are located inside the envelope at the light transmitting portion thereof. A unitary field emission structure is located inside the envelope opposite the phosphor layer, which structure comprises closely-spaced plate-like cathode and accelerator electrodes with an insulating layer separating the same. These closely-spaced electrodes may be flat or curved, as desired; convexly curved electrodes being used to increase the solid angle at which electrons are emitted from the field emission structure. The accelerator structure is formed with an array of apertures, and the cathode electrode is formed with a corresponding array of needle like members projecting into said apertures. A first voltage source is connected across the cathode and accelerator electrodes for field emission of electrons from tips of the needle-like members toward the phosphor layer. A relatively high voltage may be employed to provide for emission of electrons at a high rate and over a large solid angle from the cathode tips; the larger the voltage the greater the rate of emission and the larger the angle.
A second, higher, voltage source is connected across the cathode and anode electrodes for attraction of electrons from the field emission structure to the phosphor layer for exciting the same to luminescence. To avoid space charge limitation of current within the envelope, an annular accelerating electrode may be included adjacent the field emission structure, which electrode is supplied with the same or lower operating voltage as the anode in surface engagement with the phosphor layer.
The invention will be better understood from the following detailed description considered with the accompanying drawings.